The major objective of this research is to make significant contributions to organic chemistry and medicine through synthetic studies of the natural products with antitumor activity, including the halichondrins, the spongistatins, and the mycolactones. We believe that the power of organic chemistry, especially organic synthesis, is most effectively extended by challenging complex systems, and much of the progress of medicine certainly depends upon the extension of the power of chemistry. More specifically, research efforts will be made first to develop general, flexible, and efficient syntheses of certain natural products and then to apply these to the synthesis of their analogs and derivatives. These studies will provide clues for developing better antitumor drugs and/or will help to deliver a new anticancer drug to patients at an acceptable cost. [unreadable] [unreadable]